. . "http://www.iso.org/iso/catalogue_detail?csnumber=31894"^^ . . "http://en.wikipedia.org/wiki/Quantum_number"^^ . . "Principal Quantum Number"@en . . "The \"Principal Quantum Number\" describes the electron shell, or energy level, of an atom. The value of \\(n\\) ranges from 1 to the shell containing the outermost electron of that atom."^^ . . . . "n" .